This invention relates generally to adhesive films, more particularly to multilayer adhesive films that contain at least one barrier layer and still more particularly to the use of such multilayer films to impart water resistance to a foam carpet pad.
U.S. Pat. No. (USP) 5,612,113 discloses a carpet that has a primary backing layer from which yarn strands extend, a secondary backing layer bonded to the primary backing layer and a thin, liquid impervious layer bonded to the secondary backing layer by way of a non-aqueous thermoplastic adhesive. The adhesive may be, for example, a hot melt adhesive.
DE 4208991 discloses a plastic edge band for edging wooden furniture. The band, cut from a strip or continuous sheet, consists of at least two layers of plastic, 400-4000 micrometers (xcexcm) thick and 12-200 millimeters (mm) wide. Band preparation employs coextrusion, multiple extrusion or lamination. At least one layer must contain polypropylene homopolymer (PP), propylene copolymer, high density polyethylene (HDPE) or a mixture thereof. The layer must also contain a non-self adhesive, solvent-free, adhesive film. The adhesive film contains a polymer with acid, ester or other polar group functionality. One such polymer is an ethylene/methyl acrylate/maleic anhydride terpolymer.
JP 62-073.942 discloses a film prepared by laminating a biaxially stretched PP film and a resin layer formed from a mixture of an ethylene/propylene (EP) block copolymer resin, a petroleum resin or a terpene resin, and an ethylene/acrylic acid (EAA) copolymer resin.
J60-149,453 discloses a composite film comprising a laminated biaxially stretched PP film and a heat-sensitive adhesive resin film. The adhesive resin film is preferably an ethylene/alpha-olefin (EAO) copolymer that may be modified or graft polymerized with maleic anhydride (MAH).
EP 424,761 discloses a multilayer film that has at least mono-axial orientation. The film includes a PP core layer that is substantially free of an antiblock agent such as silica (SiO2) , at least one PP outer layer and an antiblock agent and at least one heat-laminated layer. The latter layer comprises an ethylene/vinyl acetate (EVA) copolymer, an ethylene acrylate copolymer, an EAA polymer or mixtures of the above.
The present invention is a multiple layer adhesive and barrier film that comprises at least three layers, the layers being a) a core layer having a first side and an opposing second side, b) an adhesive layer bonded to the first side of the core layer, and c) a barrier layer bonded to the second side of the core layer, the barrier layer comprising a polymer blend including a propylene copolymer and an acid anhydride grafted propylene copolymer, the core layer comprising an ethylene/alpha-olefin copolymer, and the adhesive layer comprising an ethylene copolymer that contains polar moieties and an anti-block compound.
The expression xe2x80x9cethylene homopolymerxe2x80x9d encompasses homopolymers consisting essentially of ethylene monomer units as well as ethylene polymers containing minor amounts of monomer units other than ethylene provided that such polymers have the characteristics substantially similar to an ethylene homopolymer consisting essentially of ethylene monomer units. Suitable ethylene homopolymers include linear low density polyethylene (LLDPE) and low density polyethylene (LDPE). Preferred LDPE polymers are prepared using a constrained geometry metallocene catalyst (CGC), such as those disclosed in U.S. Pat. No. 5,272,236. A commercially available and suitable LLDPE for use in the polymer blend is DOWLEX* 2247A, which is available from The Dow Chemical Company.
* means Trademark of The Dow Chemical Company. 
The multiple layer adhesive and barrier film (MLABF) of the present invention comprises at least three layers. The layers include a core layer with a first side and an opposing second side; an adhesive layer bonded to the first side of the core layer and a barrier layer bonded to the second side of the core layer. The use of first and second to designate sides of the core layer simply provides a basis to show that the adhesive layer bonds to one side of the core and the barrier layer bonds to the other side of the core.
The core layer comprises an EAO copolymer. The EAO copolymer has polymerized therein ethylene and at least one copolymerizable alpha-olefin (xcex1-olefin) monomer that contains from 3 to 20 carbon atoms (C3- 20), preferably from 3 to 8 carbon atoms (C3-8). Illustrative xcex1-olefins include propylene, butene-1, pentene-1, hexene-1, heptene-1 and octene-1. The EAO copolymer is preferably linear low density polyethylene (LLDPE). A preferred LLDPE is an ethylene/octene-1 copolymer commercially available from The Dow Chemical Company under the Trademark DOWLEX.
The core layer may further comprise a color concentrate. The color concentrate comprises an amount of pigment dispersed in a copolymer carrier. The amount of pigment desirably ranges from 50 to 70 percent by weight (wt %), based on color concentrate weight. The amount preferably ranges from 55 to 68 wt %. The color concentrate is desirably present in an amount within a range of from 10 to 20 percent by weight, based on core layer weight. The copolymer carrier must simply be compatible with the EAO copolymer of the core layer and aid in dispersing the pigment throughout the core layer. xe2x80x9cCompatiblexe2x80x9d, as used herein, means that a blend of the copolymer carrier and the EAO copolymer visually appears to contain a single phase rather than either co-continuous phases or a continuous phase and a discrete phase. Preferred carrier polymers include low density polyethylene (LDPE) and linear low density polyethylene (LLDPE).
The adhesive layer comprises an ethylene copolymer that contains polar moieties. The polar moieties of the ethylene copolymer provide a polar functionality that improves adhesion with other materials. Such ethylene copolymers include ethylene/acrylic acid (EAA) copolymer resins and graft-modified ethylene polymers, such as maleic anhydride-modified (MAH-modified) ethylene polymers, especially MAH-modified LLDPE. An EAA copolymer suitable for use in the polymer blend is PRIMACOR* 1430 (commercially available from The Dow Chemical Company). An anhydride-modified LLDPE that is suitable for use in the polymer blend is BYNEL(copyright) 4104 (commercially available from E. I. du Pont de Nemours and Company). The polar moiety-containing ethylene copolymer can be used in nearly any amount. However, the amount is preferably from 35% to about 100% by weight (wt %), based on adhesive layer weight. Amounts below 30 wt % have a diminished ability to enhance adhesion. * means Trademark of The Dow Chemical Company.
The adhesive layer preferably further comprises an anti-block concentrate. The concentrate is preferably present in an amount within a range of from 1 to 10 percent by weight, based on adhesive layer weight. Satisfactory results follow with an anti-block concentrate that comprises silicon dioxide (SiO2) in a LDPE carrier resin. An SiO2 content of from 15 to 20 percent by weight, based on concentrate weight, provides preferred results. A commercially available material meeting these criteria has a 15 wt % SiO2 content and an 85 wt % polyethylene content (CN-734 available from Southwest Plastics), the amounts totaling 100 wt %.
If the adhesive layer includes LLDPE, the adhesive layer also preferably comprises a minor amount of a processing aid, such as AMPACET(trademark) 10562, which is 3 wt % VITON(copyright) A (a fluoroelastomer available from DuPont Dow Elastomers, L. L. C.) in 97 wt % polyethylene, the percentages being based on processing aid weight and totaling 100%.
If desired, either or both of the adhesive layer and the core layer may contain one or more additives such as colorants, UV stabilizers, antioxidants and flame retardants.
The barrier layer comprises a polymer blend that comprises a propylene copolymer and an acid anhydride grafted propylene copolymer. The acid anhydride grafted propylene copolymer is preferably a maleic anhydride grafted propylene copolymer. A suitable commercially available anhydride-modified polypropylene is BYNEL(copyright) 50E571 (E. I. du Pont de Nemours and Company). The grafted copolymer is preferably present in an amount within a range of from 20 to 40 percent by weight, based on polymer blend weight. The amount is preferably about 30 weight percent. If the amount declines below 20 wt %, especially significantly below 20 wt % (as in 10 wt %), the barrier layer has a level of functionality below that needed to provide desirable results. As the amount exceeds 40 wt %, especially with amounts in excess of 50 wt %, costs increase to a point that it overwhelms desirable performance attributes of the copolymer.
The multi-layer adhesive film may serve a variety of useful purposes. One such purpose is as a barrier layer of a foam/film laminate used as a carpet pad. The carpet pad suitably comprises a cushioning foam layer that has at least two spaced-apart and generally parallel major planar surfaces. At least one of the surfaces has a multi-layer adhesive film adhered thereto in order to reduce, preferably eliminate, liquid absorption by the carpet pad.
The multiple layer adhesive films have a thickness that typically ranges from 1 mil (25 micrometers (xcexcm)) to 4 mils (100 xcexcm), and are more typically about 2 mils (50 xcexcm). While any of a number of film preparation techniques may be used to make the multiple layer adhesive films of the present invention, either a blown film extrusion process or a cast film process, yields very satisfactory results. Co-extrusion provides even more preferred results as it appears to provide better interlayer contact and bonding than alternate techniques such as casting each layer separately and then forming a multiple layer film. The films preferably have a 2% secant modulus, as determined by ASTM D882, of at least 25,000 pounds per square inch (psi) (172.4 megapascals (MPa)) at 230xc2x0 C. Although the films preferably have a modulus in the machine direction (MD) equal to that of the transverse direction (TD), skilled artisans understand that conventional film forming processes yield films with an MD modulus that exceeds the TD modulus. The 2% secant modulus is preferably at least 25,000 psi (172.4 MPa) at 23xc2x0 in any direction, whether MD or TD.